1. Field of the Invention
The present invention relates to a tape cassette provided with a reel lock mechanism for unrotatably locking reel hubs carrying a recording medium in a tape form wound therearound.
2. Description of the Related Art
In various tape cassette used for high-density recording, e.g., of video signals or PCM signals, reel lock mechanisms for unrotatably locking reel hubs have been practically used in order to prevent slackening of magnetic tapes when not used, i.e., during storage.
In the tape cassette, e.g., for VHS, Beta-Cam or 8 mm, magnetic tape is wound around reel hubs provided with flanges. The flange is provided at its outer peripheral surface with irregularities forming an engagement portion. The tape cassette is also provided with reel lock members which are movable toward and away from the engagement portions.
FIG. 5 schematically shows a reel lock mechanism, for example, employed in a Beta-Cam VTR cassette, in which magnetic tape 1 is wound around reel hubs 3 and 4 accommodated in a casing 2 which is formed of upper and lower halves. Lower flanges 3a and 4a attached to the reel hubs 3 and 4 are provided at their outer peripheral surfaces with engagement portions 3a1 and 4a1, respectively. Reel lock members 5 and 6 corresponding to the reel hubs are rotatably supported by shaft pins 2a and 2b provided in the casing, respectively. A numeral "7" indicates a lock level for inhibiting opening and closing operations of a lid provided at a front end of the casing. Rotation of the reel lock member 6 is allowed in accordance with the operation of the lock lever 7.
In an ordinary state, i.e., unused state, the reel lock members 5 and 6 are biased by coil springs 8 and 9, so that claws (engaging portions) 5a and 6a provided at their ends may contact and engage with the engagement portions 3a1 and 4a1 to unrotatably lock the reel hubs 3 and 4, respectively.
When the cassette is loaded in a recording and reproducing apparatus, lever portions 5b and 6b located at ends remote from the claws 5a and 6a are biased to rotate the reel lock members 5 and 6, so that the claws 5a and 6a move away from the engagement portions 3a1 and 4a1 to allow rotation of the reel lock hubs 3 and 4.
The reel lock mechanism thus provided in the tape cassette prevents the pay-out of the magnetic tape from the reel hub and thus the slackening thereof, and therefore prevents the damage to the magnetic tape which may be caused by the slack, when an impact is applied to the tape cassette casing in the unused state or the casing is subjected to vibration during transportation. However, certain disadvantages are caused by the reel lock mechanism utilizing the peripheral surfaces of the flanges for the locking operation.
FIG. 6 is an enlarged view showing an engaged state of the claw 5a (6a) of the reel lock member 5 (6) and the engagement portion 3a1 (4a1) of the flange 3a (4a). In this engaged state, although the reel hubs 3 and 4 are rotatably locked as described above, the reel hubs 3 and 4 (and flanges 3a and 4a) are not restricted from moving and vibrating in a direction of the thickness of the cassette casing, i.e., a direction indicated by an arrow T.
When the cassette undergoes the vibration and/or impact, e.g., during transportation, the reel hubs 3 and 4 may vibrate in the direction of the thickness of the casing, as represented by broken lines in FIG. 7.
During the vibration, the reel lock members 5 and 6 are in the locking state, and thus the claws 5a and 6a are in contact with the engagement portions 3a1 and 4a1, so that the claws 5a and 6a rub on the engagement portions 3a1 and 4a1 due to the vibration of the reel hubs 3 and 4, which may generate shaved powder. In general, the flanges 3a and 4a are formed from ABS resin or HIPS (high impact resistance polystylene) or may be formed from mixture of PC (polycarbonate) and ABS resin. Meanwhile, the reel lock members 5 and 6 are formed, e.g., from POM (polyacetal).
The reel hubs 3 and 4 may contact also with the upper and lower halves due to the vibration, so that shaved powder may be generated also between the reel hubs 3 and 4 and the upper and lower halves.
There is a high possibility that the shaved powder generated in the casing 2 adheres to the magnetic tape 1 during the recording and reproducing operations. This causes a significantly disadvantageous dropout of signals to be reproduced. Further, the shaved powder may adhere to a window provided in the casing, which impairs the external appearance of the tape cassette.